Friday, March 25, 2016

We've been following a large, and growing Lassa fever outbreak in West
Africa - first in Nigeria, then in Benin, and most recently Togo - since
early January (seeNigeria: Lassa Fever Outbreak With 40 Fatalities). Of note, the case fatality rate has been unusually high, running over 50% among lab confirmed cases.

Today the ECDC has published an 8 page PDF Rapid Risk Assessmenton the Lassa Fever outbreak in Africa, and the risks of seeing imported cases in Europe. It contains the most detailed chronology of events we've seen to date, and clears up much of the early confusion over the cases in Germany.

I've excerpted the summary and conclusions, but follow the link to download the full document.

The two imported cases of Lassa fever recently reported from Togo indicate a geographical spread of the disease to areas where it had not been recognised previously. Delays in the identification of viral haemorrhagic fevers pose a risk to healthcare facilities. Therefore, Lassa fever should be considered for any patient presenting with suggestive symptoms originating from West African countries (from Guinea to Nigeria) particularly during the dry season (November to May), a period of increased transmission, and even if a differential diagnosis such as malaria, dengue or yellow fever is laboratory-confirmed.

Case ascertainment should involve asking about consumption of foods and drinks contaminated by rodent urine or droppings and exposure to Mastomys rodents or to patients presenting with haemorrhagic fever.

Prevention of nosocomial transmission

Patients suspected of viral haemorrhagic fever should be in placed in ad-hoc isolation and cared for using appropriate personal protective equipment (PPE). Once diagnosis is confirmed, the patient should be transported to a specialised treatment centre, the competent public health authority should be notified immediately and contact tracing should be systematically initiated.

In nosocomial settings with adequate barrier nursing and prevention and control measures, the secondary attack rate for Lassa fever is extremely low.

Laboratory

Testing of samples for Lassa virus should be performed under BSL-4 laboratories. Sufficient capacity exists in the EU for testing purposes, however given the wide genetic diversity of circulating Lassa viruses, laboratory protocols for RT-PCR detection should be revised periodically.

Post exposure prophylaxis Intravenously administered ribavirin is the treatment for confirmed cases of infection with Lassa virus. Risk/benefit considerations need to be drawn carefully on a case-by-case basis. In particular, this applies to cases presenting relative contraindications for the use of ribavirin.

There is currently no evidence supporting the use of ribavirin as a post-exposure prophylaxis (PEP). Oral administration of ribavirin is currently only recommended as a precautionary measure for PEP in the event of ‘high-risk exposure’ to Lassa virus following a risk-benefit analysis. Advice to travellers

Travellers to West Africa should be informed of the risk of exposure to Lassa fever virus, particularly in areas currently experiencing outbreaks. The risk is higher in rural areas, where living conditions are basic. Travellers should avoid consumption of foods and drink contaminated by rodent droppings, exposure to rodents or to patients presenting with haemorrhagic fever.

Those travelling to these regions to provide care should be aware of the risk of exposure and should apply appropriate personal protective measures.